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ix                          TEETH OF  EARLY UNGULATES                      2O5

of forty-four teeth, the molars being of course bunodont, with the
three chief tubercles most developed. The bones of the tarsus
interlock and are not serial, as they are in many other members
of the Condylarthra. The astragalus has a shorter neck than in
Meniseotherium, for example. It has in this a likeness to the
same bone in the Amblypoda, to the primitive members of
which, such as Pantolambda, this animal bears much resemblance.
" Astragali and many skeletal bones of PeriptycJius rhabdodon and
Pantolatnbda 'bathmodon are almost indistinguishable/* observes
Mr. Matthew. The fore-feet of this genus are unknown, but it
would seem that it was plantigrade from the evidence of the hind-
feet. There are several species of the genus.

Possibly, but not at all certainly, the Mioclaenidae, -with the
genera Hfioclaenus and JProtoselene, are to be referred to this same
order of primitive Ungulates. It is only necessary to mention
them here, because they show very clearly the primitive form of
dentition of these early Eocene mammals. The teeth are quite
complete and unbroken by a diastema. The canines are but little
pronounced. The molars are not strictly tritubereular, but have a
prevailing trituberculy. The nature of the feet is not known,
Since the genus Protoselene, as its name denotes, shows an indica-
tion of a commencing selenodonty, it has been suggested that this
group is the stock whence the Artiodactyles have been derived.

In any case, whether the particular comparisons that have been
made as to the relationship of various forms of Condylarthra are
valid or not, it seems to be plain that this group represents^jfe
earliest Ungulate stock, but little differentiated from
temporaneous Creodonts.

This group of extinct mammals has the following principal
characteristics :---
They are large, semiplantigrade Ungulates, of heavy build and
apparently elephantine gait. The dentition is for the most part
complete as in other ancient groups, and the canines are in the
later forms big tusks. The back teeth are brachyodont and
ridged (lophodont). Both radius and ulna in the fore-limb, and
tibia and fibula in the hind-limb, are well developed. The bones